//Given a binary tree, return the zigzag level order traversal of its nodes' val
//ues. (ie, from left to right, then right to left for the next level and alternat
//e between). 
//
// 
//For example: 
//Given binary tree [3,9,20,null,null,15,7], 
// 
//    3
//   / \
//  9  20
//    /  \
//   15   7
// 
// 
// 
//return its zigzag level order traversal as: 
// 
//[
//  [3],
//  [20,9],
//  [15,7]
//]
// 
// Related Topics 栈 树 广度优先搜索


//leetcode submit region begin(Prohibit modification and deletion)
/**
 * Example:
 * var ti = TreeNode(5)
 * var v = ti.`val`
 * Definition for a binary tree node.
 * class TreeNode(var `val`: Int) {
 *     var left: TreeNode? = null
 *     var right: TreeNode? = null
 * }
 */
class Solution {
    fun zigzagLevelOrder(root: TreeNode?): List<List<Int>> {

    }
}
//leetcode submit region end(Prohibit modification and deletion)
